1. Field of the Invention
The present invention relates to apparatus for the interferometric measurement of light waves. More particularly, the invention pertains to apparatus of such sort fabricated in integrated optics on an anisotropic substrate.
2. Description of the Prior Art
Unbalanced optical interferometers comprise devices in which a light beam is split into at least two partial light beams. After the beams traverse defined, unequal paths, they are recombined into a single beam. As a result of interference, the intensity of the recombined beam is a function of the phase difference between the two partial light beams. Unbalanced interferometers are employed, for example, for light source wavelength stabilization, wavelength measurement, frequency analysis of light and demodulation of frequency-modulated optical signals.
A prerequisite for proper operation of such a device is maintenance of the selected optical path difference (determined as refractive index x path difference). Specifically, length and refractive index changes due to temperature change must not influence the optical path difference. In this regard, it is known to temperature-control the interferometer (that is, to actively control the temperature) to maintain it at the same temperature at all times. It is also known to construct beam-optical interferometers entirely of material of extremely low thermal expansion qualities such as Zerodur.
Current research is devoted to miniaturization and integration of optical and optoelectronic components. In integrated optics components, the light is guided in waveguides, modulated, superposed and detected. The structures consisting of waveguides and electrodes are applied to the surface of transparent substrates such as lithium niobate, various semiconductors, glass and garnet. Most of the materials employed in integrated optics (IO) are synthetic monocrystals. In such materials, thermal expansion and the thermal change of refractive index are non-negligible and of differing magnitudes in the various crystal directions. Accordingly, it has not been possible to construct an unbalanced, temperature-compensated interferometer in integrated optics by employing known, conventional techniques. Temperature control of the component is indeed conceivable; however, in most applications, it is not practicable due to the required energy consumption and the required broad temperature range.